"Therefore it seems to be united to the body by means of an incorruptible body, and such would be some heavenly light, which would harmonize the elements, and unite them together."

Metaphor in Context

OBJ 3: Further, things which are very distant from one another, are not united except by something between them. But the intellectual soul is very distant from the body, both because it is incorporeal, and because it is incorruptible. Therefore it seems to be united to the body by means of an incorruptible body, and such would be some heavenly light, which would harmonize the elements, and unite them together.
(I, Q76, A7, Obj 3)